The use of portable personal communication devices, such as cellular phones, Personal Digital Assistant (PDA), a notebook computer and/or any other movable communication devices being configured to connect to a telecommunication network in a wireless manner, has increased dramatically in recent years. Additionally, the use of portable navigational devices, such as Satellite Positioning System (SPS) receivers, has increased as these devices have become more widely available. Further technological developments have allowed the combination of an SPS receiver (e.g. a Global Positioning System (GPS) receiver) and a radio communication device in an integrated unit, such as a combination of a GPS receiver and cellular phone unit. Such combined communication end devices have many applications such as personal security, emergency response, vehicle tracking, and inventory control.
However, such combined communication end devices may also exhibit certain shortcomings such as increased power consumption and a reduced performance. One marked disadvantage inherent in many combined SPS receiver and radio communication device is the decreased performance of the SPS receiver in particular when a radio transmitter of the radio communication device is active. A common reason for such a performance reduction is self interference between the radio transmitter and the SPS receiver. Although the radio transmitter of the radio communication device and the SPS (radio) receiver typically operate in completely different frequency bands, the described self interference is often troublesome because of at least some of the following reasons: (A) The spatial distance between the radio transmitter and the SPS receiver is small. (B) The radio transmitter transmits a comparatively strong radio signal, which has to reach a base station of a cellular telecommunication network. (C) The SPS receiver is typically very sensitive, because the SPS signal level on the earth's surface is typically very small.
U.S. Pat. No. 6,107,960 discloses a method and an apparatus for reducing self or cross interference in a combined satellite positioning system receiver and communication transceiver device. A control signal is transmitted from the communication transceiver to the satellite positioning system receiver when the communication transceiver transmits data at a high power level over a communication link. The control signal causes satellite positioning system signals from satellites to be blocked from the receiving circuits of the satellite positioning system receiver, or to be disregarded by the processing circuits of the satellite positioning system receiver.
US 2007/0064835 A1 discloses measures for reducing a self interference within a communication end device comprising a radio transmitter and a radio receiver. The measures include freezing an automatic gain control loop of the radio receiver, freezing a synchronization loop, discarding channel estimation data and/or blanking received information. Certain criteria, such as a transmission power and a transmission mode may also be used to determine whether and how many measures are to be used.
U.S. Pat. No. 5,301,368 discloses a system for controlling the operation of a radio telephone and a GPS receiver in a coordinated manner. If the level of a received GPS signal is below a predefined threshold level, a control unit determines whether the radio telephone is in an ON-CALL mode (i.e. the radio telephone is transmitting) or in an OFF-CALL mode (i.e. the radio telephone is not transmitting). (A) If the radio telephone is in the OFF-CALL mode, the GPS receiver is switched on. When receiving GPS data an “Automated Gain Control” is activated. Further circuit components ensure that during GPS reception no jamming signals are transmitted by the radio transmitter of the radio telephone. However, if there is no GPS signal being received by the GPS receiver, the radio telephone is allowed to transmit radio control signals. (B) If the radio telephone is in the ON-CALL mode the GPS receiver is disabled or blanked.
The known self interference countermeasure by disabling a GPS receiver during an active radio transmitter has the disadvantage that with an increasing activity of the radio transmitter, the GPS receiver will be increasingly blanked. In particular as Long Term Evolution (LTE) technology typically implies a continuous transmission of a cellular transceiver, the known blanking solution may not work since the GPS receiver will be disabled (almost) all the time.
There may be a need for providing a mechanism, which allows (a) for an efficient reduction of self interference between a transmitting portion of a radio transceiver and a further radio receiver of a combined communication end device and (b) for a reliable reception of radio signals by the radio receiver even if the transmitting portion of the radio transceiver is mostly active.